82 Principles of Plant Culture. 



are usually thicker than slower-growing ones. We can 

 judge of the comparative vigor of nursery trees by 

 observing the length, and diameter of the intemodes. 



118. The Stem Elongates Fastest just behind the 

 growing point (66), and at least in young plants, just 

 behind the primary original growing point (55). When 

 we desire to check the growth of the stem, therefore, we 

 remove the terminal growing point by pinching (416a). 



119. Pinching Stimulates Branching because remov- 

 ing the terminal growing point stimulates the develop- 

 ment of other growing points farther back (104). 



Section VIII. The Leaves. 



We have seen that one or more leaves are normally 

 formed at each node of the stem (115). 



120. The Function of Leaves is food preparation 

 (58). Since food is prepared only in the light, the 

 cells of leaves are in most plants so arranged as to 

 best expose them to light, i. e., in thin, more or less 

 horizontal plates, which are strengthened and at the 

 same time supplied with water by a network of vascu- 

 lar bundles (67) connecting with the stem. They are 

 protected by the epidermis (64), but have access to 

 air through the stomata (65). 



Each leaf, like the stem and root, is developed from 

 one or more growing points (66), located near the base. 

 Cell division in the leaf is confined to the near vicinity 

 of the growing points, hence an injury to the older 

 part of the leaf is not repaired further than by the 

 formation of callus (72) over the wounded parts. 



